for Windows 10, you generally do not need to download third-party software, as Microsoft provides robust built-in support. How to Enable Sinhala and Tamil IME (Built-in)
Without a proper IME, typing a simple word like “කොහොමද” (kohomada) or “வணக்கம்” (Vanakkam) would be impossible. A good IME provides: Sinhala Tamil Ime Free Download Windows 10